Digital cameras and digital video camcorders are becoming more popular with consumers as a result of decreasing cost, increasing performance, and convenience. Many digital cameras on the market today produce still images having two million pixels or more, and some are capable of capturing short motion sequences of modest quality. Digital video cameras produce very high-quality digital video with bit-rates on the order of 25 million bits/second, and some can produce megapixel-resolution still images.
As these devices become more common, there will be an increased desire for transmitting digital images and digital motion sequences over the Internet. Unfortunately, even relatively low bit-rate motion sequences create large amounts of data that can be unwieldy for low-bandwidth channels such as dial-up internet connections. The transmission of such quantities of data via email may even be prohibited by certain internet service providers.
Farther into the future, the quality and duration of motion capture on digital still camcorders will gradually approach that of today's digital video camcorders. Digital still images will continue to increase in resolution, though perhaps at a slower pace. The quantity of data required to represent this imagery will increase commensurately.
On the other hand, relatively low-bandwidth devices and connections will become more numerous as small internet appliances, multimedia-capable handheld computers, cellular phones, and other wireless devices proliferate. It will be increasingly necessary, therefore, to further compress high-quality digital images and digital motion sequences for low-bit rate channels and devices. This process is sometimes referred to as transcoding. Unfortunately, there are many instances in which aggressive image compression degrades everything in the scene with equal vigor; subjects as well as background regions become obscured by severe compression artifacts, resulting in an unnatural image and an annoying viewing experience.
One can envision improved transcoding algorithms that incorporate a variety of segmentation and “image understanding” techniques in order to selectively and intelligently vary the compression ratio for each segment or object in a digital image or frame. Unfortunately, because these algorithms are conventionally invoked after the time of capture, they may be challenged by the artifacts and general loss of information caused by any initial compression.
There is a need, therefore to improve the transcoding process for digital images and digital video sequences for low bandwidth devices.